qcacld-3.0: Fix null ptr dereference in lim_process_assoc_cleanup

Currently, lim_process_assoc_cleanup does not do null validation
for sta_ds which can lead to null pointer derefrence.

Add null pointer check for sta_ds in lim_process_assoc_cleanup

Change-Id: I74ad0e11213c0bec1473984f312f18b5f1082082
CRs-Fixed: 2423883

core/mac/src/pe/lim/lim_process_assoc_req_frame.c

@@ -1893,7 +1893,7 @@ void lim_process_assoc_cleanup(struct mac_context *mac_ctx,
 
 		qdf_mem_free(assoc_req);
 		/* to avoid double free */
-		if (assoc_req_copied && session->parsedAssocReq)
+		if (assoc_req_copied && session->parsedAssocReq && sta_ds)
 			session->parsedAssocReq[sta_ds->assocId] = NULL;
 	}